The present invention relates to an actuator that sets the tilt angle of a controlled object, such as a mirror, in a desired direction. 2. Description of the Related Art
Japanese Unexamined Patent Application Publication Nos. 2002-296518, 8-334723, and 5-119280 describe so-called planar galvanomirrors. In these galvanomirrors, two moving plates are provided inside the outermost peripheral substrate, and each of the moving plates is swingably supported by a pair of torsion bars.
In the galvanomirrors described in Japanese Unexamined Patent Application Publication Nos. 2002-296518 and 8-334723, a driving mechanism for driving a mirror includes coils respectively provided on an outer moving plate and an inner moving plate, and permanent magnets provided around or on the lower side of the coils.
The galvanomirror in Japanese Unexamined Patent Application Publication No. 5-119280 is driven by utilizing electrostatic attractive force. A mirror part is supported by a substrate via a pair of torsion bars. Strain gauges are provided near the bases of the torsion bars. The tilt angle of a mirror surface is controlled while measuring changes in resistance of the strain gauges.
However, in the galvanomirrors described in Japanese Unexamined Patent Application Publication Nos. 2002-296518 and 8-334723, since the coils that form the driving mechanism are planar coils, it is structurally difficult to increase the number of turns because of size limitations. For this reason, a sufficiently great driving force cannot be obtained, and it is difficult to increase the driving velocity (responsivity) of the mirror.
In Japanese Unexamined Patent Application Publication No. 5-119280, strains caused during deformation of the torsion bars are detected from changes in resistance with the strain gauges. However, such strain gauges have a low sensitivity and easily pick noise, and therefore, the detection accuracy is low. Moreover, since the strain gauges are susceptible to temperature changes, a temperature correction circuit is needed to increase the detection accuracy. This complicates the structure.